How can I format a decimal to always show 2 decimal places in Python?

General Discussions
1

How can I format a decimal to always show 2 decimal places in Python? I want to display values like:

- 49 as 49.00
- 54.9 as 54.90

Regardless of the number of decimal places, I want to ensure that the decimal is always displayed with 2 decimal places. This is for displaying monetary values, and I would like to do this in an efficient manner.

For example, the number 4898489.00 should also be formatted properly.

2

It looks like you’re using the Decimal objects from the decimal module, which is great for handling fixed-point arithmetic. The Decimal class has a quantize() method that can round a number to a fixed number of decimal places, which is exactly what you need for formatting values like money.

Here’s a simple example:

from decimal import Decimal, Context, Inexact

# Define the precision
TWOPLACES = Decimal(10) ** -2  # This represents 0.01

# Round to two places
formatted_decimal = Decimal('3.214').quantize(TWOPLACES)
print(formatted_decimal)  # Outputs: 3.21

For validating that a number doesn't exceed two decimal places, you can use the Inexact trap, which will raise an exception if the number has more than two decimal places:
try:
    Decimal('3.214').quantize(TWOPLACES, context=Context(traps=[Inexact]))
except Inexact:
    print("Number exceeds two decimal places.")

Additionally, to maintain two decimal places across your application, you can rely on string conversion after rounding:
formatted_string = str(Decimal('10.00'))
print(formatted_string)  # Outputs: 10.00
3

You can format your decimal values directly with string formatting:

value = 49
formatted_value = "{:.2f}".format(value)
print(formatted_value)  # Outputs: 49.00
4

Python 3.6+ supports f-strings, which provide a concise and efficient way to format strings:

value = 54.9
formatted_value = f"{value:.2f}"
print(formatted_value)  # Outputs: 54.90